This invention relates to devices having gas-phase deposited coatings and their methods of production. More specifically, this invention relates to devices, and their method of production, having gas-phase deposited coatings which are non-fouling and wettable.
The chemical composition of surfaces plays a pivotal role in dictating the overall efficacy of many devices. Some devices require non-fouling, and wettable surfaces in order for the devices to be useful for their intended purposes. For example, many biomedical devices such as catheters, stents, implants, interocular lenses and contact lenses require surfaces which are biologically non-fouling, which means that proteins, lipids, and cells will not adhere to the surfaces of the devices. In some cases materials for devices are developed which have all the necessary attributes for their intended purposes, such as, strength, optimal transmission, flexibility, stability, and gas transport except that the surfaces of the materials will foul when in use. In these cases either new materials for the devices are developed or an attempt to change the surface characteristics of the materials is made.
In the specific case of contact or interocular lenses, particularly contact lenses, although many polymeric materials possess the necessary mechanical, oxygen permeation and optical properties required for lens manufacture, many potential contact lens materials are subject to rapid biological fouling due to the adhesion of proteins, lipids, and other molecules present in the tear fluid surrounding the lens, and/or the surface energies of the materials are too low making the contact lenses too hydrophobic, and therefore not wettable by the tear fluid.
In light of the above considerations, a common approach utilized by various researchers is to attempt to improve the biocompatibility of the potential contact lens materials by application of a thin coating to these substrates. In theory such a coating would take advantage of the inherent favorable bulk mechanical, gas transport and optical properties of the polymer with the applied coating providing the required hydrophilicity and non-fouling properties. However, despite the plethora of such studies, it is significant to note that, at present, not a single contact lens manufacturer offers commercial products having coatings applied for this express purpose. Obviously, although the concept of simply applying a surface coating to remedy physical property deficiencies of a given polymer substrate has theoretical appeal, this has proven to be a totally illusive goal in actual practice. The previous failures reflect the fact that, to be commercially viable, a successful contact lens coating procedure must satisfy a myriad of rather stringent requirements. These requirements, as a minimum, include the following criteria: the coatings must be uniform and, ideally, pin-hole free; the coatings must be both wettable and non-biologically fouling; the coatings should be essentially devoid of extractables and they must exhibit long-term chemical stability in aqueous saline solution; the coatings must exhibit excellent optical transparency in the visible region of the electromagnetic spectrum; the coatings must not compromise the oxygen permeability (i.e., the so-called DK value) of the polymer substrate; and, in the case of reusable lenses, the coatings must exhibit sufficient abrasion resistance and chemical stability to withstand repeated cleanings. In the latter case, cleaning procedures would include both exposure to harsh chemical cleansing agents and to mechanical rubbing actions.
European Patent Application 93810399.1, filed Jun. 2, 1993, describes a complicated multi-step process to alter the surface of a contact lens material. The process requires a plasma treatment of the surface to generate surface free radicals, which are reacted with oxygen to form hydroperoxy groups, to which are graft polymerized an ethylenically unsaturated monomer plus cross-linking agent, followed by a solution extraction period to remove unreacted monomers. This complex process requires the presence of inhibition agents during the monomer coupling reactions to prevent the homopolymerization of the ethylene monomers by free radicals generated during the thermal decomposition of the hydroperoxy groups.
The plasma deposition of triethylene glycol monoallyl ether is reported in the German patent application DE19548152.6. Although it did not deal with contact lenses, it centered on surface modifications to reduce the adsorption of biological compounds. Coatings of such type would be useful in reducing non-specific protein adsorption on certain biosensor surfaces. In this work, substrates for coating were located outside the plasma discharge zone and exceptionally low RF power densities were employed in an attempt to minimize fragmentation of the polyethylene oxide units present in this monomer. Not unexpectedly, coatings deposited in the relatively non-energetic region upstream of the plasma discharge and outside the luminous discharge zone were only weakly attached to the underlying substrates. Another problem encountered in this work was the low volatility of the monomer. This resulted in a requirement for monomer heating to provide sufficient vapor for the plasma deposition process. However, even with heating, the vapor pressures obtainable without initiating thermal decomposition of the monomer were too low to provide any sort of flow rate and/or reactor pressure controllability. Additionally, the unusually low vapor pressure resulted in exceptionally low film deposition rates with accompanying film non-uniformity. The coatings obtained were not tested for adhesion under flow conditions, nor were they subjected to any abrasive cleaning or rubbing actions. Simple soaking of the coating substrates in distilled water for relatively short periods (e.g., less than 48 hours) resulted in measurable changes in the chemical compositions of the coatings as revealed by XPS surface analysis of these coatings before and after the simple water immersion test.
U.S. Pat. Nos. 3,008,920 and 3,070,573 reveal the use of plasma surface treatments to generate free radicals for subsequent peroxy group formation followed by the grafting of vinylic monomers to the polymer substrate. The control of the depth uniformity and density of the grafted coatings is a difficult problem encountered in these grafting experiments.
PCT/US90/05032 (Int. Publication #W091/04283) discloses increasing the wettability of polymeric contact lens materials synthesized from specific hydroxy acrylic units and vinylic siloxane monomers by grafting other molecules to the surface. The only examples of the proposed grafting procedure described in this patent involve attachment of specific polyols by wet chemical procedures, but this patent does suggest that hydroxy acrylic units may be grafted to the specific hydroxy acrylic/siloxane polymeric materials by radiation methods. Additionally, radiation induced attachment by gaseous hydroxyl acrylic units was described in U.S. Pat. No. 4,143,949 as a means of improving surface hydrophilic character.
U.S. Pat. No. 4,143,949 discloses a process for putting a hydrophilic coating on a hydrophoic contact lens. The polymerization is achieved by subjecting a monomer, in gaseous state, to the influence of electromagnetic energy, of a frequency and power sufficient to cause an electrodeless glow discharge of the monomer vapor.
U.S. Pat. No. 4,693,799 describes a process for producing a plasma polymerized film by pulse discharging. The process comprises forming a plasma polymerized film on the surface of a substrate placed in a reaction zone by subjecting an organic compound containing gas to plasma polymerization utilizing low temperature plasma formed by pulse discharging, in which the time of non-discharging condition is at least 1 msec, and the voltage rise time for gas breakdown is not longer than 100 msec. Specifically, the patent disclosed a process employing an alternating current (xe2x80x9cACxe2x80x9d) electrical discharge operated in a pulsed mode to provide films having small coefficients of friction and high lubricity for use on magnetic tapes and discs. Although various experimental sets were carried out at different AC frequencies (from 2 to 2 Khz), all experiments within a given set were reportedly conducted at fixed plasma on to plasma off times. However, it provides no mention of the film compositional control available via changes in the ratio of plasma on to plasma off times during pulsed plasma polymerization of an organic monomer; nor is any mention made of the adhesion of the deposited films with respect to soaking or abrasive cleaning actions.
U.S. Pat. Nos. 3,854,982 and 3,916,033 describe the use of liquid coating techniques to improve the wettability of contact lens polymers. In these procedures free radical polymerizable precursors, including hydroxy alkyl methacrylates, are attached to contact lenses by exposure to high energy radiation. However, these solution attachment processes provide poor control of the film thickness and these films exhibit poor abrasion resistance, particularly when attached to polysilicone substrates.
The direct plasma treatment to improve the wettability of contact lenses is described in U.S. Pat. No. 3,925,178 in which an electrical or radio frequency discharge in water vapor is employed for that purpose. This non-coating treatment results in a relatively unstable hydrophilic surface in which the wettability of the contact lens substrate decreases rapidly in time.
U.S. Pat. No. 5,153,072 describes a method of controlling the chemical structure of polymeric films by plasma deposition and films produced thereby. The focus of this invention involves controlling the temperature of the substrate and the reactor so as to create a temperature differential between the substrate and reactor such that the precursor molecules are preferentially adsorbed or condensed on the substrate either during plasma deposition or between plasma deposition steps.
Yasuda et al., xe2x80x9cSome Aspects of Plasma Polymerization Investigated by Pulsed R.F. Discharge,xe2x80x9d Journal of Polymer Science: Polymer Chemistry Edition, Vol. 15, pp. 81-97 (1977), discloses the polymerization of organic compounds in glow discharge (plasma polymerization) by using pulsed RF discharge (100 microsec. on, and 900 microsec off). The effect of pulsed discharge on polymer deposition rate, pressure change in plasma, ESR signals of free spins in both plasma polymer and substrate, and the contact angle of water on the plasma polymer surface were investaged for various organic compounds.
Nakajima et al., xe2x80x9cPlasma Polymerization of Tetrafluoroethylene,xe2x80x9d Journal of Applied Polymer Science, Vol. 23, pp. 2627-2637 (1979), describes the plasma polymerization of tetrafluoroethylene in both continuous wave and pulsed radio frequency (xe2x80x9cRFxe2x80x9d) discharges. They reported that both polymer deposition rates and polymer structures were essentially identical when using continuous wave and pulsed RF discharge.
Lopez et al., xe2x80x9cGlow discharge plasma deposition of tertraethylene glycol dimethyl ether for fouling-resistant biomaterial surfaces,xe2x80x9d Journal of Biomedical Materials Research, Vol. 26, pp 415-439 (1992), discloses the glow discharge plasma deposition of tetraethylene glycol dimethyl ether onto glass, polytetrafluoroethylene and polyethylene. The monomer required heating, and low power to retain the ethylene oxide content of the plasma deposited coatings. As a result, no monomer flow rate controllability was available, and the films deposited at the lower RF powers exhibited low stability to even simple overnight soaking in water. The film adhesion to the polymeric substrate could be improved by carrying out the plasma deposition at higher power but this improved adhesion was achieved at the expense of loss of ethylene oxide film content and thus poorer non-fouling properties.
The need still remains for a composition which can be applied to the surface of a substrate to provide a film of coating that is uniform in thickness, pin-hole free, optically transparent in the visible region of the magnetic spectrum, permeable to oxygen, biologically non-fouling, relatively abrasive resistant, and wettable (hydrophilic).
The present invention provides a device comprising a substrate and a coating composition, the coating composition being formed by the gas phase or plasma polymerization of a gas comprising at least one organic compound or monomer, the organic compound having the following structure: 
where Y represents Cxe2x95x90O;
R1, R2, R3, R4, R5, R6 and R7 each independently represents:
H,
OH,
halogen,
C1-C4 alkyl,
C1-C4 alkene,
C1-C4 diene,
C1-C4 alkyne,
C1-C4 alkoxy, or
C1-C4 alkyl halide; and
R8 represents:
H,
halogen,
C1-C4 alkyl,
C1-C4 alkene,
C1-C4 diene,
C1-C4 alkyne,
C1-C4 alkyl halide,
C1-C4 aldehyde,
C1-C4 ketone,
C1-C4 epoxide,
C1-C4 carboxylic acid,
C1-C4 ester,
xe2x80x94CHxe2x95x90CHR9, where R9 is H, halogen, C1-C4 alkyl, C1-C4 alkyl halide, C1-C4 aldehyde, C1-C4 ketone,
C1-C4 alkoxyl, C1-C4 epoxide, C1-C4 carboxylic acid, or C1-C4 ester, or
xe2x80x94OR10, where R10 is H, halogen, C1-C4 alkyl, C1-C4 alkene, C1-C4 diene, C1-C4 alkyne, C1-C4 alkyl halide, C1-C4 aldehyde, C1-C4 ketone, C1-C4 epoxide, C1-C4 carboxylic acid, or C1-C4 ester.
The polymerization of the present invention can be carried out using a pulsed discharge having a duty cycle of less than about ⅕, in which the pulse-off time is less than about 2000 msec and the pulse-on time is less than about 100 msec. The duty cycle can also be varied, thus the coating composition can be gradient layered accordingly.
The compound generally has low molecular weight, one or more ether linkages and at least one unsaturated carbon-carbon bond.
The devices of this invention have coating compositions which are uniform in thickness, pin-hole free, optically transparent in the visible region of the magnetic spectrum, permeable to oxygen, abrasive resistant, wettable and biologically non-fouling; therefore, making it possible to use substrates which, except for their surface characteristics, are well suited for their intended uses. In the specific case of contact or interocular lenses, particularly contact lenses, substrates which are not wettable by the tear fluid, which are subject to rapid biological fouling, and/or have surface energies which are too low can be made useful when coated with the coating compositions of this invention.
The coatings of the present invention are deposited on the surface of a solid substrate via plasma polymerization of at least one selected monomer. The plasma deposition of the present invention is achieved by either continuous wave (xe2x80x9cCWxe2x80x9d) or pulsed plasmas. In the pulsed mode, the deposition is carried out of a fixed plasma duty cycle or, alternately, using a variable duty cycle pulsed plasma deposition.